Free body diagrams isolate the object completely from its surroundings
There are a few strategies you can use to draw free body diagrams:
First draw the compass points and decide on a suitable scale
then draw as ketch of the object isolated form it surroundings
Locate, with a point, the approximate centre of the object
From the point, draw a force vector to represent each force acting on the object
Note: do NOT include forces that the object exerts on other objects
F.B.D can also be drawn to scale the length of the vectors represents the actual size of the force. A scale must be added by the drawing (1 cm = N)
WE use F.B.D to be able to find the resultant forces.
Section 2.2 and 2.3 (From Ayesha) Section 2.2: Mass and the Force of Gravity
Mass
Weight
Definition
The amount of matter in an object
The term used to describe the force of gravity that a celestial body, as Earth, exerts on a mass
SI Unit
Kilograms (kg)
Newton (N)
Direction
No direction.
Always directed towards the center of the Earth.
Force of Gravity
The force of attraction between two objects in the universe.
Force of gravity between an object and a planet depends on:
Mass of planet
Mass of object
Distance between the centres of the two objects
Mass always remains constant, but the weight can change due to the following factors:
Altitude: weight is greater at lower elevations, while lower at higher elevations.
Latitude: weight is greater at the poles and lower at the equator. The reason is the Earth’s bulging appearance at the equator due to its rotation and shape.
Newton’s Law of Universal Gravitation
The force of gravity between two masses in the universe is directly proportional to the product of the masses and inversely proportional to the square of the distance between the centres.
It can be written as:
FG = Gm1m2 / d2
Where:
G is the gravitational constant= 6.67 x 10-11 N.m2 / kg2
m1= mass of the Earth in kg
m2 = mass of the other object in kg
∆ d = distance between the centres, in metres
NOTE: What causes the tides? http://www.pbs.org/wgbh/nova/venice/tide_flash.html
Section 2.3: Gravitational Field Intensity Force field: region of space where a force exists due to the presence of an object
Example: region around a planet where gravity exists due to the planet’s mass. Gravitational Field Intensity:
Amount of force of gravity (weight) that the Earth exerts per unit mass of an object.
The Earth’s gravitational field intensity is 9.8 N/kg [towards centre of Earth] or [down].
The symbol for gravitational field intensity is the small letter, g.
The amounts used to calculate the Earth gravitational field intensity by using the Newton’s law of universal gravitation are:
G = 6.67 x 10-11 N. m2/kg2
Mass of Earth= 5.98 x 1024 kg
Distance= 6.38 X 106 m
Through the value of g = 9.8 N/kg [down], the weight or the force of gravitation on the object can be calculated by using the formula: Force of gravity = mass of the object x gravitational field intensity
Fg = mg
Gravitational Field Strength: (cont'd)
Gravitational field intensity (g) varies over the surface of Earth due to latitude, altitude and due to density differences in the Earth. Table 2.2
Can detect large masses of greater density (mass) in crust with a gravimeter (used in mineral exploration).
When we are larger distances away from the Earth, we get a rapid decrease in g. Table 2.3
2.4 Acceleration due to gravity
Galileo investigated freely falling objects showing all objects fell (accelerated toward the Earth) at the same rate (ignoring air friction) Calculated the acceleration due to gravity by rolling balls down a ramp
found it to be 32 ft/sec2 = 9.8 m/s2
acceleration due to gravity = 9.8m/s2 [down]
we can use the kinetic equations to analyse the motion of free falling objects.
THESE ARE NOTES FOR CHAPTER THREE: 3.1 Horizontal Motion and Friction Reviewed: Kinematics: -Mathematical descriptions or motion - Galileo New information:
Dynamics: Why do things move the way they do? Friction a Force that opposes motion whenever one surface moves or tends to move with reference to another. Types of Friction:
Sliding Friction : surface sliding past another.
Rolling Friction : Opposes the motion of on surface rolling over another.(E.g. Tire rolling on ground)
Fluid Friction: Moving through a gas or liquid ( air resistance, drag)
Limiting Static Friction à When surfaces are not sliding past. Resistance to the surface if motion.
Kinematic Friction: The forces that oppose the motion of an object once it is moving.
Vocabulary used to talk about the friction we want to occur include: Traction, Tread Etc. Places where it is desired: - Between us and the outside world. Places where it is undesired: - Moving large objects - Internally in moving objects Normal Force: A supporting force acting perpendicular to the surface. (Doesn’t have to be vertical) Example a person moving down needs friction to push it up to stop from moving. (Remember: Force of gravity always goes towards the center of the Earth. ) Ff varies FN : If there is large normal force the friction force is large as well and the opposite is true. For example, if we were trying to move Mr. Cote and a student in our class we would need more force to move him than we would need to move the student. However, if Mr. Cote was on roller blades and the student wasn’t, it’d be easier to move him so there would need to be more force on the student to move them.
Acceleration and the Force of Gravity
Pg 56-57
Notes(From Cote)
IMPORTANT: All bolded words are definitions from the glossary, if you do not understand the word look at the glossary for the meaning of the word
Fundamental Forces
1) Gravitation (Gravity): most used
2) Magnetic/Electric(Electromagnetic Force): most used
3) Strong Nuclear Force
4) Weak Nuclear Force
Order of strength(from greatest to least)
1) Strong Nuclear – nucleus of a atom
2) Electromagnetic – Infinite distance
3) Weak Nuclear - Atom
4) Gravitational – Infinite distance
Forces:
· Change object shape
· Speed object up
· Slow object down
· Change object direction of travel
· Start object moving
· Stop object moving
Units – Newton(N)
Vector – has a direction associated
- push or pull where [Forward, backward, up, down]
Measure force – through the deformation of a spring (spring scale)
- dial scale
Hello dear Physicists. In most of my posts I will be posting very informative videos and articles. Most of them will be pretty advanced but will be able to create a better understanding of today's world. Enjoy
Shrodinger's Cat: http://www.youtube.com/watch?v=CrxqTtiWxs4
Different Levels of Dimension: part 1 http://www.youtube.com/watch?v=JkxieS-6WuA part 2 http://www.youtube.com/watch?v=ySBaYMESb8o&feature=channel
The smallest of all and most expensive experiment of all? String Theory and something related to chapter 2 part 1(WATCH THIS!) http://www.youtube.com/watch?v=E7FV9aaiwKQ part 2 http://www.youtube.com/watch?v=WT_IVdCO4ZE&feature=related part 3 http://www.youtube.com/watch?v=g7bakDI_TwA&feature=related part 4 http://www.youtube.com/watch?v=tLd0lwQrxOw&feature=related part 5 http://www.youtube.com/watch?v=lWGb-pIAQ-E&feature=related part 6 http://www.youtube.com/watch?v=nD9vwfl2xQs&feature=related part 7 http://www.youtube.com/watch?v=6PVjNlXj2WQ&feature=related part 8 http://www.youtube.com/watch?v=ZuK9Rb-tBBg&feature=related part 9 http://www.youtube.com/watch?v=4BRhjntvGoE&feature=related part 10 http://www.youtube.com/watch?v=2zgxvGaei6o&feature=related part 11 http://www.youtube.com/watch?v=hB6lW-8CwpM&feature=related
CONTINUED:
Free body diagrams (F.B.D)
- Free body diagrams isolate the object completely from its surroundings
There are a few strategies you can use to draw free body diagrams:F.B.D can also be drawn to scale the length of the vectors represents the actual size of the force. A scale must be added by the drawing (1 cm = N)
WE use F.B.D to be able to find the resultant forces.
Section 2.2 and 2.3 (From Ayesha)
Section 2.2: Mass and the Force of Gravity
The force of attraction between two objects in the universe.
Force of gravity between an object and a planet depends on:
- Mass of planet
- Mass of object
- Distance between the centres of the two objects
Mass always remains constant, but the weight can change due to the following factors:- Altitude: weight is greater at lower elevations, while lower at higher elevations.
- Latitude: weight is greater at the poles and lower at the equator. The reason is the Earth’s bulging appearance at the equator due to its rotation and shape.
Newton’s Law of Universal GravitationThe force of gravity between two masses in the universe is directly proportional to the product of the masses and inversely proportional to the square of the distance between the centres.
It can be written as:
FG = Gm1m2 / d2
Where:
G is the gravitational constant= 6.67 x 10-11 N.m2 / kg2
m1= mass of the Earth in kg
m2 = mass of the other object in kg
∆ d = distance between the centres, in metres
NOTE: What causes the tides?
http://www.pbs.org/wgbh/nova/venice/tide_flash.html
Section 2.3: Gravitational Field Intensity
Force field: region of space where a force exists due to the presence of an object
Example: region around a planet where gravity exists due to the planet’s mass.
Gravitational Field Intensity:
Amount of force of gravity (weight) that the Earth exerts per unit mass of an object.
The Earth’s gravitational field intensity is 9.8 N/kg [towards centre of Earth] or [down].
The symbol for gravitational field intensity is the small letter, g.
The amounts used to calculate the Earth gravitational field intensity by using the Newton’s law of universal gravitation are:
G = 6.67 x 10-11 N. m2/kg2
Mass of Earth= 5.98 x 1024 kg
Distance= 6.38 X 106 m
Through the value of g = 9.8 N/kg [down], the weight or the force of gravitation on the object can be calculated by using the formula:
Force of gravity = mass of the object x gravitational field intensity
Fg = mg
Gravitational Field Strength: (cont'd)
Gravitational field intensity (g) varies over the surface of Earth due to latitude, altitude and due to density differences in the Earth. Table 2.2
Can detect large masses of greater density (mass) in crust with a gravimeter (used in mineral exploration).
When we are larger distances away from the Earth, we get a rapid decrease in g. Table 2.3
2.4 Acceleration due to gravity
Galileo investigated freely falling objects showing all objects fell (accelerated toward the Earth) at the same rate (ignoring air friction) Calculated the acceleration due to gravity by rolling balls down a ramp
found it to be 32 ft/sec2 = 9.8 m/s2
acceleration due to gravity = 9.8m/s2 [down]
we can use the kinetic equations to analyse the motion of free falling objects.
THESE ARE NOTES FOR CHAPTER THREE:
3.1 Horizontal Motion and Friction
Reviewed:
Kinematics:
-Mathematical descriptions or motion
- Galileo
New information:
Dynamics: Why do things move the way they do?
Friction a Force that opposes motion whenever one surface moves or tends to move with reference to another.
Types of Friction:
- Sliding Friction : surface sliding past another.
- Rolling Friction : Opposes the motion of on surface rolling over another.(E.g. Tire rolling on ground)
- Fluid Friction: Moving through a gas or liquid ( air resistance, drag)
- Limiting Static Friction à When surfaces are not sliding past. Resistance to the surface if motion.
- Kinematic Friction: The forces that oppose the motion of an object once it is moving.
Vocabulary used to talk about the friction we want to occur include: Traction, Tread Etc.Places where it is desired: - Between us and the outside world.
Places where it is undesired: - Moving large objects
- Internally in moving objects
Normal Force: A supporting force acting perpendicular to the surface. (Doesn’t have to be vertical) Example a person moving down needs friction to push it up to stop from moving.
(Remember: Force of gravity always goes towards the center of the Earth. )
Ff varies FN : If there is large normal force the friction force is large as well and the opposite is true. For example, if we were trying to move Mr. Cote and a student in our class we would need more force to move him than we would need to move the student. However, if Mr. Cote was on roller blades and the student wasn’t, it’d be easier to move him so there would need to be more force on the student to move them.